Last night I was thinking that he needed dual filter chambers. It's hard to tell with the dark photos making everything inside the filter hard to see but I think you're right, the filter does have dual chambers. They do seem small though and won't be able to handle that much flow if the media is restrictive (e.g., too fine).
I was looking at the specs for the Marineland wet/dry filters and the single chamber models are rated for a max of 700 gph while the dual chambered ones are rated for 1400 gph. This is consistent with my experience that the typical single chamber wet/dry filter will only handle ~600 gph.